Systems and methods for thermal battery control

ABSTRACT

Methods and system for operating a thermal storage device of a vehicle system are provided. In one example, a method comprises estimating a temperature of a thermal battery after the battery and coolant included therein have reached thermal equilibrium, and determining a state of charge of the battery based on the estimated temperature and one or more chemical properties of two phase change materials included within the battery. Specifically, the thermal battery may include two phase change materials with different melting points for providing thermal energy to warm coolant in a vehicle coolant system.

BACKGROUND AND SUMMARY

To enhance warming of various vehicle system components, thermal energystorage devices have been developed to store thermal energy produced bythe vehicle system for later use. These thermal storage devicestypically include a phase change material (PCM) that may store asignificant amount of thermal energy as latent heat at the phase changetemperature of the PCM. In one example approach disclosed in US2004/0154784, phase change materials such as paraffin wax may beincluded in the interior of a vehicle to conserve energy while providingheat to the passenger compartment.

However, the inventors herein have recognized potential issues with suchsystems. Specifically, estimates of the state of charge of such thermalstorage devices may be significantly reduced at the phase changetemperature of the PCM in systems including only one type of PCM.Because of the latent heat stored in the PCM at its phase changetemperature, it may be difficult to estimate the state of charge of thePCM when the PCM is transitioning between phases at its phase changetemperature. Further, even in thermal storage devices including morethan one PCM, such as the device disclosed in US 2014/0079978, theaccuracy of estimates of the state of charge may be reduced when thetemperature of coolant exiting the thermal storage device is differentthan the temperature of the thermal storage device.

For example, the temperature of the coolant exiting the thermal storagedevice may be different than the temperature of the thermal storagedevice when the coolant is not warmed to the temperature of the thermalstorage device. This may occur when the coolant entering the thermalstorage device is significantly colder than the thermal storage device,such that the thermal storage device cannot warm the coolant fast enoughto bring it to thermal equilibrium with the thermal storage devicebefore the coolant exits the thermal storage device. Thus, the coolantmay not remain in the thermal storage device for long enough to reachthermal equilibrium with the thermal storage device. As such, thetemperature of the coolant exiting the thermal storage device may notreflect the actual temperature of the thermal storage device. Therefore,when estimating the state of charge of the battery based on thetemperature of coolant exiting the battery, the accuracy of suchestimates may be reduced.

As one example, the issues described above may be addressed by a methodcomprising estimating a temperature of a thermal battery after thebattery and coolant included therein have reached thermal equilibrium,and determining a state of charge of the battery based on the estimatedtemperature and one or more chemical properties of phase change materialincluded in the thermal battery. The temperature of the thermal batterymay be estimated based on outputs from a temperature sensor coupled to acoolant outlet of the battery, where the sensor may be configured tomeasure a temperature of coolant exiting the battery.

In another example, a method for an engine cooling system may comprisestopping coolant flow through a thermal storage device comprising twophase change materials with different melting points for a duration,resuming coolant flow through the thermal storage device after theduration and estimating a temperature of coolant exiting the thermalstorage device based on outputs from a temperature sensor positionedproximate a coolant outlet of the device, and calculating a state ofcharge of the device based on the estimated coolant temperature and oneor more chemical properties of the phase change materials. Additionally,the duration may comprise an amount of time for coolant included withinthe device and internal components of the device including the phasechange materials, to reach thermal equilibrium, and where the durationmay be calculated based on a most recent coolant temperature measurementand a most recent state of charge estimate of the battery.

In yet another example, a thermal battery system may comprise a thermalstorage device including a first phase change material having a firstphase change temperature and a second phase change material having asecond, different phase change temperature. The thermal battery systemmay further comprise a coolant valve adjustable between a first positionand a second position to selectively couple the thermal storage deviceto an engine coolant circuit and regulate an amount of coolantcirculating through the thermal storage device. Additionally, thethermal battery system may comprise a temperature sensor for estimatinga temperature of the device, and a controller with non-transitorycomputer readable instructions for: estimating a temperature of thedevice when coolant within the device has stopped for more than athreshold duration, and determining a state of charge of the batterysystem based on the estimated temperature and one or more chemicalproperties of the phase change materials. In some examples, the firstand second phase change materials may be combined together in a mixture.However, in other examples, the first and second phase change materialsmay be separated from one another into distinct battery cells.

In this way, the accuracy of estimates of the state of charge of athermal battery may be increased by temporarily stopping coolant flowthrough the thermal battery until the battery, its internal components,and coolant included therein, have reached thermal equilibrium. Byresuming coolant flow after the coolant and battery have reached thermalequilibrium, and measuring coolant temperature of coolant exiting thebattery that is at the temperature of the thermally equilibratedbattery, a more direct and accurate measurement of the batterytemperature and therefore state of charge may be obtained.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A shows a schematic of an example vehicle system including athermal management system.

FIG. 1B shows a schematic of the thermal management system of FIG. 1A,including a thermal storage device.

FIG. 2A shows a first example of the thermal storage device of FIG. 1B.

FIG. 2B shows a second example of the thermal storage device of FIG. 1B.

FIG. 2C shows a third example of the thermal storage device of FIG. 1B.

FIG. 2D shows a fourth example of the thermal storage device of FIG. 1B.

FIG. 2E shows a fifth example of the thermal storage device of FIG. 1B.

FIG. 3 shows a flow chart of an example method for regulating a state ofcharge of a thermal storage device.

FIG. 4 shows a flow chart of a first example method for determining astate of charge of the thermal storage device.

FIG. 5 shows a second example method for determining a state of chargeof the thermal storage device.

FIG. 6 shows a third example method for determining a state of charge ofthe thermal storage device.

FIG. 7 shows a graph depicting changes in coolant flow through a thermalstorage device based on engine operating conditions.

DETAILED DESCRIPTION

The following description relates to systems and methods for regulatingthe state of charge of a thermal battery. A thermal battery such as thethermal battery shown in FIGS. 2A-2E may be included in a vehiclesystem, such as the vehicle system shown in FIG. 1A, to store excessheat produced by the vehicle system for later use. For example, thethermal energy stored by the thermal battery may be used in a thermalmanagement system, such as the thermal management system shown in FIG.1B, to heat various vehicle components such as a vehicle engine, cabincompartment, etc. Specifically, heat from the thermal battery may betransferred to various vehicle components via coolant circulated throughthe thermal battery. However, as coolant flows through the thermalbattery and captures heat from the thermal battery, the temperature andtherefore state of charge of the battery may decrease. To charge thebattery, excess heat produced by the vehicle system, such as heat fromexhaust gasses, may be used to warm the thermal battery. FIG. 3 showsexample control methods for regulating the state of charge of thebattery. The state of charge of the battery may be inferred based on atemperature of the coolant as it exits the thermal battery.

However, under certain conditions, such as when coolant is flowingthrough the thermal battery and the coolant entering the thermal batteryis at a significantly different temperature than the thermal battery,the coolant may not remain in the thermal battery long enough to reachthermal equilibrium with the battery. That is, although the temperatureof the coolant may increase as it flows through the thermal battery, thetemperature of the coolant may still remain lower than the temperatureof the thermal battery after exiting the thermal battery.

Thus, as shown in the example method of FIG. 4, the state of charge ofthe battery may be estimated when the coolant temperature reaches thatof the thermal battery. In other examples, such as the example shownmethod shown in FIG. 5, coolant flow through the thermal battery may betemporarily stopped until the coolant temperature of coolant in thethermal battery reaches the temperature of the thermal battery. Coolantflow may then resume and the temperature of the coolant exiting thethermal battery may be measured to estimate the state of charge of thebattery. Examples changes in coolant flow through the thermal batteryare shown in FIG. 7.

FIG. 1A shows an example embodiment of a motor vehicle 2 including athermal management system 100 in accordance with the present disclosure.Vehicle 2 includes drive wheels 6, a passenger cabin 4, and an internalcombustion engine 10. Internal combustion engine 10 includes at leastone combustion chamber (not shown) which may receive intake air via anintake passage 46 and may exhaust combustion gases via exhaust passage48. Engine 10 may be included in a motor vehicle such as a roadautomobile, among other types of vehicles. In some embodiments, engine10 may be included in a propulsion system that also includes a batterydriven electric motor, such as in a Hybrid Electric Vehicle (HEV) or aPlug-in Hybrid Electric Vehicle (PHEV). In some embodiments, thermalmanagement system 100 may be included in an Electric Vehicle (EV) whereengine 10 is omitted.

Thermal management system 100 may include a thermal storage device 50 orthermal battery 50. Several embodiments of the thermal battery 50 areshown and described in detail below with reference to FIGS. 1B-2E. Asshown in FIGS. 1A and 1B, thermal management system 100 may be coupledto engine 10, exhaust passage 48 and passenger cabin 4. The thermalstorage device 50 may be configured to capture and store heat generatedby engine 10 using one or more phase change materials (PCMs).Specifically, heat from exhaust gasses flowing through exhaust passage48 may be transferred to the thermal storage device 50, and stored forlater use. Heat from the thermal storage device 50 may then be used, forexample, to provide heat to engine 10 at a cold start, to warm passengercabin 4 in response to a passenger request to heat the cabin, etc.Additionally, in some examples, the thermal storage device 50 may beconfigured to generate heat via reversible exothermic and endothermicchemical reactions.

FIG. 1A further shows a control system 14 of vehicle 2. Control system14 may be communicatively coupled to various components of engine 10 andthermal management system 100 to carry out the control routines andactions described herein. As shown in FIG. 1A, control system 14 mayinclude an electronic digital controller 12. Controller 12 may be amicrocomputer, including a microprocessor unit, input/output ports, anelectronic storage medium for executable programs and calibrationvalues, random access memory, keep alive memory, and a data bus.

As depicted, controller 12 may receive input from a plurality of sensors16, which may include user inputs and/or sensors (such as transmissiongear position, transmission clutch position, gas pedal input, brakeinput, transmission selector position, vehicle speed, engine speed, massairflow through the engine, ambient temperature, intake air temperature,etc.), climate control system sensors (such as coolant temperature,antifreeze temperature, adsorbent temperature, fan speed, passengercompartment temperature, desired passenger compartment temperature,ambient humidity, etc.), and others.

Further, controller 12 may communicate with various actuators 18, whichmay include engine actuators (such as fuel injectors, an electronicallycontrolled intake air throttle plate, spark plugs, transmissionclutches, etc.), thermal management system actuators (such as airhandling vents and/or diverter valves, valves controlling the flow ofcoolant, valves controlling flow of refrigerant, blower actuators, fanactuators, pump actuators, etc.), and others. In some examples, thestorage medium may be programmed with computer readable datarepresenting instructions executable by the processor for performing themethods described below as well as other variants that are anticipatedbut not specifically listed.

FIG. 1B depicts a schematic diagram of an example embodiment of thermalmanagement system 100. Thermal management system 100 comprises twocircuits, heat exchange circuit 101 and coolant circuit 102. Heatexchange circuit 101 includes thermal storage device 50, coolant heatexchange loop 103 and heat recovery loop 104. Coolant circuit 102includes engine circuit 105 and heater circuit 106. Thermal energy fromexhaust gasses flowing through exhaust passage 48 may be transferred tofluid in heat recovery loop 104. The heated fluid in heat recovery loop104 may then be directed through the thermal storage device 50 to warmand/or charge the thermal storage device 50. Thus, the thermal storagedevice may capture and/or store thermal energy obtained from hot exhaustgasses. As such, energy that would have otherwise been lost to theatmosphere may be recycled and used in the thermal management system100. In this way, the fuel efficiency of the system 100 may beincreased. The thermal energy captured by the thermal storage device 50may then be used to warm various vehicle components such as engine 10,heater core 137, passenger cabin (e.g., passenger cabin 4 shown in FIG.1A). Specifically, thermal energy from the thermal storage device 50 maybe transferred to various vehicle components via coolant, circulatedthrough the thermal storage device 50. As the coolant flows through thethermal storage device 50, it is warmed, and the warmed coolant may thenbe pumped to the various vehicle components via coolant circuit 102.

Heat exchange circuit 101 may employ thermal storage device 50 tocapture thermal energy from exhaust gasses flowing through exhaustpassage 48 via heat recovery loop 104. Heat recovery loop 104 mayinclude heat exchangers 111 and 119, valve 120 and pump 121. Valve 120and pump 121 may be controlled by signals from controller 12. That is,controller 12 may send signals to valve 120 and/or pump 121 to adjustoperation thereof. Specifically, the controller 12 may adjust an openingof the valve 120 and/or a speed of the pump 121 to control an amount offluid flowing through the loop 104. In some examples, the valve 120 maybe a continuously variable valve. However, in other examples, the valve120 may be a binary valve. The pump 121 may be a variable speed pump. Byincreasing an opening of valve 120 and/or increasing a speed of pump121, fluid flow in heat recovery loop 104 between heat exchanger 111 andheat exchanger 119 may be increased. In this way, thermal energy inexhaust passage 48 may be transferred to fluid flowing through heatexchanger 119. After being warmed by the exhaust gasses in exhaustpassage 48, fluid in the loop 104 may flow through the thermal storagedevice 50, specifically through heat exchanger 111, and may transferthermal energy to the thermal storage device 50.

Thus, heat from exhaust gasses may be transferred to coolant in coolantcircuit 102 and various vehicle components, by first transferring heatfrom the exhaust gasses to the thermal storage device 50 via fluidcirculating between the thermal storage device 50 and the exhaustpassage 48. Heat in the thermal storage device 50 may then betransferred to the coolant in coolant circuit 102 by flowing the coolantin coolant circuit 102 through heat exchange loop 103 positioned withinthermal storage device 50.

Heat exchange loop 103 includes valve 117, which may be adjusted by thecontroller 12 to regulate an amount of coolant flowing through thethermal storage device 50 and heat exchange loop 103. In some examples,the valve 117 may be a three way valve, where the valve may be adjustedto a first position, where substantially no coolant flows through heatexchange loop 103, and may instead only flow through coolant line 118directly towards pump 133 without flowing through thermal storage device50. The valve 117 may be further adjusted to a second position wheresubstantially all of the coolant in coolant circuit 102 flows throughthe heat exchange loop 103 and thermal storage device 50, andsubstantially no coolant flows through coolant line 118. In someexamples, the valve 117 may be a continuously variable valve and may beadjusted to any position between the first position and the secondposition.

By adjusting the valve between the first position and the secondposition, an amount of coolant flowing through the thermal storagedevice 50 may be adjusted. Specifically, the amount of coolant flowingthrough the heat exchange loop 103 relative to coolant line 118 may beincreased by adjusting the valve 117 towards the second position, andaway from the first position. In response to a demand for increasedcoolant temperature, such as during an engine cold start, controller 12may send signals to the valve 117 to adjust towards the second position,to increase the amount of coolant flowing through the thermal storagedevice 50. As such, a temperature of the coolant may be increased byflowing the coolant through the thermal storage device 50. In this way,the thermal storage device 50 may provide an additional source of heatfor the coolant, when desired.

In some examples, the heat exchange loop 103 may additionally includevalve 124 which may regulate an amount of coolant flowing out of thethermal storage device 50, and back to the coolant circuit 102. Thus,the valve 124 may be adjusted to a closed first position wheresubstantially no coolant flow there-through, and thus, coolant flowthrough the thermal storage device 50 and heat exchange loop 103 stops.Additionally, the valve 124 may be adjusted to a fully open secondposition, where coolant flows there-through. In some examples, the valve124 may be a continuously variable valve and may be adjusted to anyposition between the first and second positions, to regulate an amountof coolant exiting the valve 124. Specifically, the controller 12 maysend signals to the valve 124 to adjust the position of the valve. Theamount of coolant flowing through the valve 124 may increase as anopening formed by the valve 124 increases with increasing deflection ofthe valve 124 towards the open second position and away from the closedfirst position.

After exiting the thermal storage device 50, coolant may be directedtowards pump 133 due to the suction generated at an inlet of the pump133. Thus, coolant may be pumped from one or more of coolant line 118and heat exchange loop 103 to various vehicle components such as engine10, by pump 133. More simply, pump 133, may circulate coolant throughcoolant circuit 102.

It should also be appreciated that in some examples, coolant in coolantcircuit 102 may not be routed through the thermal storage device 50, andthat a separate fluid flowing loop may be included in the thermalmanagement system 100 to capture heat stored in thermal storage device50. In such examples, a separate heat exchange loop, such as heatrecovery loop 104 may be used to transfer heat from the thermal storagedevice 50 to the coolant in coolant circuit 102. Thus, fluid flowingthrough this separate heat exchange loop may be routed through thethermal storage device 50 to capture heat from the thermal storagedevice 50. An additional pump may be included in the heat exchange loopto pump the fluid through the thermal storage device 50. The fluid inthis loop may then transfer heat from the thermal storage device 50 tocoolant in the coolant circuit 102 via a heat exchanger, such as heatexchanger 119. As such, coolant in coolant circuit 102 may not passthrough the thermal storage device 50, and may instead pass through aheat exchanger, where heat captured from the thermal storage device 50by a fluid flowing in a separate heat exchange loop may be transferredto the coolant.

A temperature sensor 112 may be coupled to the heat exchange loop 103for estimating a temperature of the thermal storage device 50.Specifically, the temperature sensor 112 may be coupled at a coolantoutlet of the thermal storage device 50 where coolant leaves the thermalstorage device 50. Thus, the temperature sensor 112 may be configured tomeasure a temperature of the coolant in heat exchange loop 103 as itexits the thermal storage device 50. Based on signals received from thetemperature sensor 112, the controller 12 may infer a state of charge ofthe thermal storage device 50. However, in other examples, thetemperature sensor 112 may be coupled directly to the thermal storagedevice 50 for measuring a temperature thereof. The state of charge ofthe thermal storage device 50 may be proportional to the temperature ofthe device 50. That is, the state of charge may increase with increasingtemperatures of the device 50.

The thermal storage device 50 may include housing 107. Variousinsulating materials may be included within housing 107 to maintain thetemperature of the thermal storage device 50. Further, the thermalstorage device 50 includes phase change material (PCM) 116. In someexamples, as shown below with reference to FIGS. 2D-2E, two distinctPSMs with different melting temperatures may combined to form a mixturein the thermal storage device 50. However, in other examples, as shownbelow with reference to FIGS. 2B-2C, the two PCMs with different meltingtemperatures may be separated from one another into distinct cells.

In some embodiments, as depicted in FIG. 1B, thermal storage device 50may additionally be configured to generate thermal energy throughchemical adsorption. In such examples, where the thermal storage deviceis capable of generating thermal energy, the thermal energy device 50may include a plurality of adsorber cells 122, which may be filled withan adsorbent. The adsorbent may be a high energy medium density such assilica gel, zeolite, activated carbon, or other suitable adsorbents. Theadsorbent may be formed into a crystalline structure within adsorbercells 122. Additionally, the thermal storage device 50 may include afluid container 108, fluidically coupled to the adsorber cells 122 viaelectronic throttling valve 109. Electronic throttling valve 109 may beopened or closed in response to signals from controller 12. Fluidcontainer 108 may contain an adsorbate that results in an exothermicreaction when combined with the adsorbent in adsorber cells 122. Forexample, in embodiments where the adsorber contains an adsorber such aszeolite, the fluid in fluid container 108 may be water, or an aqueoussolution, such as ethylene glycol solution or propylene glycol solution.The fluid may also be a methanol or ammonia based solution. Upon openingof electronic throttling valve 109, fluid from fluid container 108 mayenter adsorber 107, where the fluid may be adsorbed by the adsorbent.

Thermal storage device 50 may further include pressure relief valve 113.When included, fluid container 108 may further include fluid levelsensor 114, and may be coupled to fan 115.

From the coolant line 118 and/or heat exchange loop 103, coolant may bepumped by pump 133 to one or more vehicle components such as engine 10.Pump 133 may be controlled by signals from controller 12. Thus, thecontroller 12 may send signals to the pump 133 to adjust a speed of thepump 133, and therefore an amount of coolant flowing through the coolantcircuit 102. Specifically, the pump 133 may in some examples be avariable speed pump.

As depicted in the example of FIG. 1B, coolant may be pumped from one ormore of coolant line 118 and/or heat exchange loop 103 to engine circuit105. However, it should be appreciated that in other examples, coolantmay be pumped to the engine circuit 105 before being pumped to the heatexchange loop 103. It should also be appreciated, that in some examples,coolant may be pumped directly from the thermal storage device 50 tovarious vehicle components such as heater core 137, and may bypass theengine 10. Thus, coolant warmed by the thermal storage device 50 may berouted directly to a vehicle component, such as a passenger cabin (e.g.,passenger cabin 4 shown in FIG. 1A), to warm the vehicle component.

Engine circuit 105 includes, engine cooling jacket 130, radiator 131,and coolant reservoir 132. Radiator fan 134 may be coupled to radiator131. A temperature sensor may be coupled to engine 10 or engine coolingjacket 130, such as thermocouple 135. In a scenario when the engine iscold (e.g., cold-start conditions), heat stored in thermal storagedevice 50 may be transferred to coolant engine circuit 105 via heatexchanger 110 through activation of pump 133 and the adjusting of thevalve 117 to the second position. If the engine is overheated, coolantmay be circulated by pump 133 through engine cooling jacket 130, withexcess heat discharged through radiator 131 with the use of radiator fan134. In such examples, it may not be desired to warm the coolant incoolant circuit 102, and as such valve 117 may be adjusted to the firstposition and thus, coolant may bypass the thermal storage device 50.Heat from engine 10 may also be used to charge and/or heat the thermalstorage device 50 through activation of pump 121 and the opening ofvalve 120.

Heating circuit 106 includes valve 136 and heater core 137. A fan 138may be coupled to heater core 137. A passenger may request heat forpassenger cabin 4. In response to this request, controller 12 may signalvalve 136 to open, thereby partially bypassing engine circuit 105.Coolant in engine circuit 105 may be circulated through heater loop 106by activating pump 133. Heat from the coolant may then be transferred toheater core 137 and blown into passenger cabin 4 by activating fan 138.If the coolant in engine circuit 105 is insufficient to charge heatercore 137, additional heat may be passed to coolant circuit 102 byadjusting valve 117 to the second position, and flowing coolant throughthe thermal storage device 50. More detailed methods for usage andcontrol of thermal management system 100 are discussed below and withregards to FIGS. 3, 4, and 5.

FIGS. 2A-2E show example schematics of a thermal battery 202 that may beincluded in a vehicle system (e.g., motor vehicle 2 shown in FIG. 1A).Thus, the thermal battery 202 shown in FIGS. 2A-2E, may be the same orsimilar to thermal storage device 50 described above with reference toFIG. 1B. Further, FIGS. 2A-2E may be described together in thedescription herein. After being introduced in the description of one ofthe FIGS. 2A-2E, components of the battery 202 may not be reintroducedor described again. Thermal battery 202 may be included in a vehiclesystem to store heat produced by an engine (e.g., engine 10 shown inFIGS. 1A and 1B) of the vehicle system for later use in the vehiclesystem. Specifically, heat from the thermal battery 202 may betransferred to coolant of a coolant system (e.g., coolant circuit 102shown in FIG. 1B) by flowing the coolant through the thermal battery202. When the temperature of the coolant is less than the temperature ofthe thermal battery 202, heat may be transferred from the thermalbattery 202 to the coolant flowing through the thermal battery 202,draining or discharging the battery 202. In the description herein,draining or discharging the battery may refer to the removal of heat orthermal energy from the battery 202. Similarly, charging the battery mayrefer to the increase of thermal energy of battery 202. To charge thebattery 202, excess heat produced by the vehicle system, such as fromthe engine, may be transferred to the thermal battery 202, as explainedabove with reference to FIG. 1B.

Focusing on FIG. 2A, it shows a schematic 200 of a first embodiment ofthe thermal battery 202. The thermal battery 202 may comprise a housing204, within which components of the thermal battery 202 may be included.A heat exchange region 206 is included within the housing 204, and mayinclude two different PCMs with different melting points. However, inother examples, more or less than two PCMs, each with different meltingpoints may be included in the heat exchange region 206. In someexamples, as shown below with reference to FIGS. 2B and 2C, the PCMs maybe contained within distinct cell blocks, and may be separated from oneanother. However, in other examples as shown below with reference toFIGS. 2D and 2E, the PCMs may be combined to form a mixture in the heatexchange region 206.

One or more insulating layers, such as insulating layer 203, may beincluded between the housing 204 and the heat exchange region 206 toreduce heat transfer between the interior and exterior portions of thehousing 204 and battery 202. Thus, the insulating layer 203 may reduceheat loss from the thermal battery 202 to the external environment.Although only one insulating layer is shown in FIG. 2A, it should beappreciated that more than one layer may be included. Further, theinsulating layers may be constructed from any suitable insulatingmaterial. Each layer may be constructed from the same or differentinsulating material.

Heat from exhaust gasses flowing in an exhaust passage (e.g., exhaustpassage 48 shown in FIGS. 1A and 1B) may be introduced to the thermalbattery 202 via a heat source inlet tube 206. In some examples, asdescribed above with reference to FIG. 1B, the heat from exhaust gassesmay be transferred to the thermal battery 202 via a fluid. Thus, in someexamples, a fluid at a higher temperature than the thermal battery 202,may flow through the heat source inlet tube 206 and into the thermalbattery 202 to provide thermal energy (e.g., heat) to the thermalbattery 202. However, it should be appreciated that in other examplesexhaust gasses may be directly routed to the thermal battery 202 andintroduced thereto through the heat source inlet tube 206. After flowingthrough the heat source inlet tube 206, fluids (e.g., liquids and/orgasses) may flow through a series of heat exchange tubes 208 positionedwithin the heat exchange region 206, where heat from the fluid may betransferred to the PCM in the heat exchange region 206. Thus, the PCMmay absorb heat from the fluid flowing through the heat exchange tubes208, assuming the fluid is at a higher temperature than the PCM. Fluidin the heat exchange tubes 208 may then exit the thermal battery 202 viaa heat source outlet tube 210. Thus, the inlet tube 206 and outlet tube210 may provide fluidic communication between exterior portions of thebattery 202 and the heat exchange region 206.

Coolant from the coolant system may enter the thermal battery 202 via acoolant inlet tube 212. After flowing through the inlet tube 212,coolant may proceed through heat absorption tubes 214 positioned withinthe heat exchange region 206, where heat from the PCM in the heatexchange region 206 may be transferred to the coolant in the heatabsorption tubes 214. Thus, coolant may absorb heat from the PCM,assuming the coolant is at a lower temperature than the PCM. Coolant inthe heat absorption tubes 208 may then exit the thermal battery 202 viaa coolant outlet tube 216. Thus, the inlet tube 212 and outlet tube 216may provide fluidic communication between exterior portions of thebattery 202 and the heat exchange region 206.

Although the inlet and outlet tubes 206 and 210 are shown in FIG. 2A tobe positioned at and extending through the same side of the thermalbattery 202, it should be appreciated that in other examples, the inletand outlet tubes 206 and 210 may be positioned on different sides of thebattery 202. For example, the inlet tube 206 may be positioned at andmay extend through front end 205 of battery 202, and outlet tube 216 maybe positioned at and extend through back end 207 and vice versa.

Similarly, the inlet and outlet tubes 212 and 216 although shown in FIG.2A to be positioned and extending through the same side of the thermalbattery 202, may in other examples be positioned on different sides ofthe battery 202. For example, the inlet tube 212 may be positioned atand extend through front end 205 and outlet tube 216 may be positionedat and extend through back end 207, and vice versa.

Heat source inlet tube 206, heat source outlet tube 210, and heatexchange tubes 208 are included in the thermal battery 202. However, forthe purposes of simplicity, the tubes 206, 208, and 210 are omitted fromthe embodiments of the thermal battery 202 shown below with reference toFIGS. 2B-2E. Thus, it is important to note that despite being omittedfrom FIGS. 2B-2E, tubes 206, 208, and 210 are still included in theembodiments of the thermal battery 202 shown in FIGS. 2B-2E. Thus, thebattery 202 may be heated/charged by flowing heated fluid through theheat exchange tubes 208. Further, the battery 202 may becooled/discharged by flowing coolant through the heat absorption tubes214.

Turning now to FIGS. 2B-2E, they show different embodiments of thethermal battery 202. In the embodiments of the thermal battery 202 shownin FIGS. 2B and 2C, the two different PCMs may be encapsulated indistinct cells. However, in FIGS. 2D and 2E, the two different PCMs areshown mixed together in the heat exchange region 206.

Focusing first on FIG. 2B, its shows a first schematic 225 of a secondembodiment of the battery 202, where the heat absorption tubes 214 maybe positioned in a sinuous, stacked configuration. Each of the tubes 214may be separated by a gap 226, in which cells containing the PCM may bepositioned. The heat exchange region 206 may include a first set ofcells 218 containing a first PCM 220, and a second set of cells 222containing a second PCM 224. Although the first set of cells 218 andsecond set of cells 222 are shown positioned in an alternating order inFIG. 2B, it should be appreciated that other arrangements and/orordering of the cells 218 and 222 are possible. Further, although anapproximately even number of cells 218 and 222 are shown in FIG. 2B, itshould be appreciated that the number of cells 218 relative to cells 222included in the heat exchange region may be altered. As depicted in FIG.2B, the cells 218 and 222 may be filled with PCM. However, in otherexamples, any number, or all of the cells 218 and 222 may be onlypartially filled with PCM. Thus, the amount of PCM included in each ofthe cells 218 and 222 may be varied.

Further, although the first set of cells 218 are shown in FIG. 2B toonly include the first PCM 220 and the second set of cells 222 are shownto only include the second PCM 224, it should be appreciated that thecells 218 and 222 may contain a mixture of the two PCMs 220 and 224 inany relative amounts. Further, the relative amounts of the first andsecond PCMs 220 and 224 included in the first set of cells 218 may bedifferent than the second set of cells 222. That is the first set ofcells 218 and second set of cells 222, may both include the first PCM220 and second PCM 224, however, the first set of cells 218 may comprisea greater amount of the first PCM 220 relative to the second PCM 224than the second set of cells 222, or vice versa.

The first PCM 220 and the second PCM 224 may have phase changetemperatures that are different by 5° F. In the description herein thephase change temperature may refer to the temperature at which amaterial changes phase such as between liquid and solid, and/or betweenliquid and gas, and/or in some examples, between solid and gas. Thetemperature at which a material changes between a liquid and a gas maybe referred to as the vaporization phase change temperature, and thetemperature at which a material changes between a liquid and a solid maybe referred to as the solidification phase change temperature. However,the difference in the phase change temperatures of the two PCMs 220 and224 may be in a range between 3-15° F. For example, the first PCM 220may have a melting temperature of 207° F. and the second PCM 224 mayhave a melting temperature of 212° F. However, in other examples, thefirst PCM 220 may have a melting temperature in a range of temperaturesbetween 60° C. and 115° C. Further, the second PCM 224 may have amelting temperature in a range of temperatures between 60° C. and 115°C. However, in some examples, the phase change temperatures of the PCMs220 and 224 may depend on a concentration of glycal in the PCMs 220 and224, and/or on ambient pressure. The phase change temperatures of thePCMs 220 and 224 may decrease for increases in altitude and decreases inambient pressure. Further the phase change temperatures of the PCMs 220and 224 may increase with increasing concentrations of glycal. As such,the phase change materials may be selected for their phase changetemperature at altitude. For example, the phase change temperatures ofthe PCMs 220 and 224 may be limited to below 90° C. to reduce and/orprevent evaporation of the PCMs 220 and 224 at lower ambient pressures,such as at higher altitudes. Further, the glycal concentration of thePCMs 220 and 224 may be adjusted to change the phase change temperaturesof the PCMs. However, in all examples, the phase change temperatures ofthe two PCMs 220 and 224 may be separated by approximately 3-15° C.

Thus, the phase change temperatures of the first PCM 220 and second PCM224 may not overlap. Said another way, the temperatures at which thefirst PCM 220 and second PCM 224 change phase, are different. Forexample, the first PCM 220 may change phase between a solid and a liquidat a different temperature and/or range of temperatures than the secondPCM 224. It is important to note, that in some examples, the phasechange temperature of a given PCM may not always be the same, and thatthe phase change temperature may vary depending on conditions in thethermal battery 202 such as ambient pressure. Specifically, the phasechange temperatures of the PCMs 220 and 224 may vary depending on anamount of super saturation and an ambient pressure.

However, the phase change temperatures of the first PCM 220 and secondPCM 224 may be sufficiently separated from one another such that therange of temperatures over which the PCM 220 may change phase isdifferent and does not overlap with the range of temperatures over whichthe PCM 224 may change phase. In this way, the first PCM 220 and secondPCM 224 may not change phase simultaneously. That is, the first PCM 220may not undergo a phase change while the second PCM 224 is undergoing aphase change, and vice versa. As explained above, a phase change mayrefer to the process in which a material such as PCM changes between asolid and liquid, liquid and gas, and/or solid and gas.

Thus, by selecting PCMs with different phase change temperatures, heattransfer between the two different PCMs may be increased, and as such amore uniform temperature of the thermal battery may be achieved. Saidanother way, the thermal battery may reach thermal equilibrium morequickly by including two PCMs with different phase change temperaturesthan in examples where the thermal battery only includes one PCM with asingle phase change temperature.

Further, by including the two PCMs with different phase changetemperatures, a measurable temperature of the thermal battery 202, maybe continuous over the charge states of the thermal battery 202. Thatis, there may be a distinct measurable temperature for every differentstate of charge of the battery 202. Said another way, a given measurabletemperature of the battery 202, may correspond to a specific state ofcharge of the battery 202. However, it is important to note that thestate of charge of the battery 202 may be additionally determined basedon whether the battery is charging or discharging, a rate of change inthe temperature of the battery 202, a coolant temperature, etc., asexplained in greater detail below with reference to FIGS. 3-5.

For example, when the temperatures of the first PCM 220 and second PCM224 are below their phase change temperature, and thermal energy isadded to the battery 202 during charging of the battery 202, thetemperature of the PCMs 220 and 224 may increase. The temperatures ofthe two PCMs 220 and 224 may continue to increase as thermal energy isadded to the battery 202, until the temperature of the first PCM 220reaches its phase change temperature. Thus, since the first PCM 220 mayhave a lower phase change temperature than the second PCM 224, the PCM220 may change phase before the second PCM 224 when charging the battery202 from a starting temperature below the phase change temperatures ofthe two PCMs 220 and 224. As the PCMs continue to absorb thermal energy,the temperature of the first PCM 220 may remain approximately the same,as it changes phase. However, the second PCM 224 may continue toincrease in temperature depending on the configuration of the battery202, and chemical properties of the PCMs 220 and 224. For example, whenthe PCMs are combined to form a mixture, as shown below in the examplesof FIGS. 2D and 2E, the PCMs 220 and 224 may warm at approximately thesame rate due to nearly instantaneous heat transfer between the two PCMs220 and 224. Specifically, in examples where the PCMs 220 and 224 arecombined together into a mixture, the rate of heat transfer between thePCMs 220 and 224 may be nearly instantaneous and may depend only ondiffusion rates, and time for individual molecules and/or elementswithin the PCMs 220 and 224 to diffuse/orient themselves to their newphase structure (e.g., glass/crystalline structure when changing fromliquid to solid). Thus, the second PCM 224 may remain at the phasechange temperature of the first PCM 220 when the first PCM 220 undergoesa phase change while heat is added to the battery 202, until the firstPCM 220 has completed the phase change. Then, one the first PCM 220 hascompleted its phase change, both of the PCMs 220 and 224 may continue toincrease at a nearly uniform rate as heat is added to the battery 202.

However, in examples where the first and second PCMs 220 and 224 areseparated from one another into distinct battery cells 218 and 222 asshown in the examples of FIGS. 2B and 2C, energy may not transferimmediately between the PCMs 220 and 224, and the second PCM 224 maywarm above the phase change temperature of the first PCM 220 while thefirst PCM is undergoing a phase change and energy is being added to thebattery 202. Energy from the second PCM 224 may be transferred to thefirst PCM 220 to warm the first PCM 220 and establish thermalequilibrium in the system. Thus, the warming of the second PCM 224during the phase change of the first PCM 220 may be limited. However,the rate of heat transfer between the first and second PCMs 220 and 224may depend on the rates of conduction and/or convention in the battery202 in examples where the first and second PCMs 220 and 224 areseparated from one another into distinct cells. Thus it is important tonote, that the thermal battery 202 may not be in thermal equilibriumwhen the enthalpy of the battery 202 is changing. Specifically, thebattery 202 may not be in thermal equilibrium when one of the PCMs 220and 224 is undergoing a phase change, as the other PCM not undergoing aphase change may continue to change in temperature while the PCMundergoing the phase change may remain at a constant temperature due todelayed heat transfer between the PCMs 220 and 224. As such, thetemperatures of the PCMs may be different in such examples, and thebattery 202 may not be in thermal equilibrium. It is also important tonote that the PCMs even when not undergoing phase changes, may be atdifferent temperatures than one another during charging and/ordischarging of the battery 202 due to different molecular propertiesthat may affect the specific heat of the PCMs, and or rates ofconduction there-through, etc. Thus, the amount of time for the battery202 to reach thermal equilibrium may depend on the internal heattransfer rates of the battery 202, such as diffusion rates, molecularalignment rates, latent heat, conduction rates, convection rates, etc.,and may also depend on the rate of change of enthalpy in the battery 202(e.g., the rate of charging and/or discharging).

When the first PCM 220 has completed it phase change, and the battery202 continues to be charged, one or more of the first and second PCMs220 and 224 may continue to increase in temperature, and/or the secondPCM 224 may begin to change phase. In some examples, the phase changetemperature of the second PCM 224 may be such that the second PCM 224begins its phase change when the first PCM 220 ends its phase change.However, in other examples, the first and second PCM 220 and 224 maycontinue to increase in temperature after the phase change of the firstPCM 220. When the temperature of the second PCM 224 reaches its phasechange temperature, it may begin to change phase at a relativelyconstant temperature. Meanwhile, the first PCM 220 may continue toincrease in temperature, assuming it has completed its phase change.Similar to where the first PCM 220 changes phase, if the temperature ofthe first PCM 220 is higher than the second PCM 224 when the second PCM224 undergoes its phase change, thermal energy from the first PCM 220may transfer to the second PCM 224, accelerating the phase change. Thereverse is true as the battery 202 is discharged from a fully chargedstate. The fully charged state may be where both the first and secondPCM 220 and 224 are above their phase change temperature. In someexamples, the fully charged state may a charge state of the battery 202,where the first and second PCMs 220 and 224 are both in liquid phase.However, in other examples, the fully charged state may a charge stateof the battery 202, where the first and second PCMs 220 and 224 are bothin gaseous phase.

Thus, by including the two PCMs with different phase changetemperatures, the state of charge of the battery 202 may be continuousover a temperature range including the phase change temperatures of thetwo PCMs 220 and 224. That is, every state of charge of the battery 202may correspond to a distinct measurable temperature. Thus, the accuracyof estimates of the state of charge of the battery 202 including twoPCMs with different phase change temperatures may be increased relativeto systems including only one PCM. In systems with only PCM, the stateof charge of the battery 202 may be any state of charge in a range ofstate of charges of the battery at the phase change temperature of thePCM. That is, due to the latent heat of the PCM at its phase changetemperature, the state of the charge of the battery 202 may vary at thephase change temperature of the PCM depending on where the PCM is in itsphase change.

In some examples, the battery 202 may optionally include a firsttemperature sensor 230 that may be configured to measure a temperatureof the first PCM 220. Specifically, the temperature sensor 230 may bedisposed in one of the first set of cells 218, for measuring atemperature of the first PCM 220. Similarly, a second temperature sensor232 may be included in the battery 202 and may be configured to measurea temperature of the second PCM 224. Specifically, the temperaturesensor 232 may be disposed in one of the second set of cells 222 formeasuring a temperature of the second PCM 224. The temperature sensors230 and 232 may be electrically coupled to a controller (e.g.,controller 12 shown in FIGS. 1A and 1B), for communicating a measuredtemperature of the PCMs 220 and 224 to the controller.

Thus in some examples, the controller may estimate a state of charge ofthe battery 202 based on temperatures of the first and second PCMs 220and 224. When the temperature of one of the PCMs at its phase changetemperature, the state of charge of the battery 202 may be estimatedbased on the temperature of the other PCM not undergoing a phase change.In this way, a more accurate estimate of the state of charge of thebattery 202 may be achieved, since the temperature of the PCM notundergoing the phase change may be different depending on the enthalpyof the PCM undergoing the phase change. More simply, the temperature ofthe PCM not undergoing the phase change may correlate to a specificenthalpy of the PCM undergoing the phase change, and therefore a stateof charge of the battery 202.

However, in other examples, as explained below with reference to FIGS. 3and 4, the state of charge of the battery 202 may be estimated based ona coolant temperature of coolant exiting the battery 202 via the outlettube 216, after the battery 202 has reached thermal equilibrium. Thus,when coolant flow in the battery 202 has stopped and/or stagnated forlong enough for the coolant, and components of the battery 202 to reachthermal equilibrium, coolant flow may then resume, and a temperature ofthe stagnated coolant exiting the battery 202 may be estimated based onoutputs from the temperature sensor 112. A state of charge of thebattery 202 may then be estimated based on the coolant temperature. Assuch, the temperature of coolant exiting the battery 202 may moreaccurately reflect the temperature of the battery 202, and therefore theaccuracy of estimates of the state of charge of the battery 202 that areobtained based on the temperature of the exiting coolant may beincreased.

The PCMs 220 and 224 may comprise any suitable phase change materials.For example, the PCMs 220 and 224 may comprise any one or more ofparaffin wax blends, water, bath metals, plain thermals, etc.

Turning now to FIG. 2C, it shows a schematic 250 of a third embodimentof the battery 202, where the coolant flows around the PCMs 220 and 224.The third embodiment of the battery 202 shown in FIG. 2C may beidentical to the second embodiment shown in FIG. 2B, except that in FIG.2C, the heat absorption tubes 214 may be positioned around the PCMs 220and 224 instead of between the PCMs as shown in FIG. 2B. Specifically,the heat absorption tubes 214 may be positioned around the cells 218 and222, between the cells 218 and 222 and the insulating layer 203.

Moving on to FIG. 2D, it shows a schematic 275 of a fourth embodiment ofthe battery 202, where the cells 218 and 222 may be omitted, and thePCMs 220 and 224 may be combined to form a mixture 224. Thus, the fourthembodiment of the battery 202 shown in FIG. 2D may be identical to theembodiment shown in FIG. 2B, except that the PCMs may not be containedin cells and may instead be distributed approximately evenly throughoutthe heat absorption region 206. The mixture 224 may be included in theheat absorption region 206. In some examples, the mixture 224 may beconfined to only a portion of the heat absorption region 206. However,in other examples, as shown in FIG. 2D, the mixture 224 may coverapproximately the entire heat absorption region 206. As such, the heatabsorption region 206 may be defined by a fluid barrier, which mayseparate the inside of the absorption region 206 from the outside, andmay contain the mixture 224. As explained above with reference to FIG.2B, the mixture 224, may contain any relative amounts of the two PCMs220 and 224 (not shown in FIG. 2D). In some examples, the mixture 224may comprise approximately 75% of the first PCM 220 and 25% of thesecond PCM 224. However, in other examples, the mixture 224 may compriseapproximately 50% of the first PCM 220 and 50% of the second PCM 224. Inyet further examples, the mixture 224 may comprise approximately 25% ofthe first PCM 220 and 75% of the second PCM 224.

However, the relative amounts of the PCMs 220 and 224 may be varied asdesired. By varying the relative amounts of the PCMs, the thermal energystorage of the battery 202 may be biased towards a higher or lowertemperature. For example, when a greater amount of the first PCM 220 isused than the second PCM 224, a greater amount of latent heat may beavailable at a lower temperature since the phase change temperature ofthe first PCM 220 may be lower than that of the second PCM 224.Conversely, when a greater amount of the second PCM 224 is used than thefirst PCM 220, a greater amount of latent heat may be available at ahigher temperature since the phase change temperature of the second PCM224 may be higher than that of the first PCM 220.

Further, the concentration of the PCMs may be varied throughout the heatabsorption region 206. For example, the concentration of the PCMs mayincrease radially outwards from a center of the battery 202. In otherexamples, the concentration of the PCMs may decrease radially outwardsfrom the center of the battery 202. However, other patterns orconcentration distributions of the PCMs may be utilized, such asGaussian. Further, the concentration distributions of the two PCMs 220and 224 may be different and/or independent of one another. However, inother examples the concentration distributions of the two PCMs 220 and224 may be approximately the same.

Moving on to FIG. 2E, it shows a schematic 290 of a fifth embodiment ofthe battery 202 that may be identical to the fourth embodiment of thebattery 202 shown in FIG. 2D, except that the tubes 214 may bepositioned around the mixture 224, similar to that shown in FIG. 2C,instead of within the mixture 224 as shown in FIG. 2D. Thus, the heatabsorption tubes 214 may be positioned around a perimeter of the heatabsorption region 206, between the heat absorption region 206 andinsulating layer 203.

Continuing to FIG. 3, it shows an example method 300 for regulating astate of charge of a thermal battery (e.g., thermal storage device 50shown in FIGS. 1A and 1B, and thermal battery 202 shown in FIGS. 2A-2E).As explained above with reference to FIG. 1A-2B, the thermal battery maybe charged via heat from exhaust gasses flowing through an exhaustpassage (e.g., exhaust passage 48 shown in FIGS. 1A and 1B) of an engine(e.g., engine 10 shown in FIGS. 1A and 1B). The thermal energy capturedby one or more PCMs of the thermal battery (e.g., PCMs 220 and 224 shownin FIGS. 2B and 2C) may then be transferred to coolant as the coolantflows through the battery. Specifically, as described above withreference to FIG. 1B, one or more of a heat source valve (e.g., valve120 shown in FIG. 1B), and a heat source pump (e.g., pump 121 shown inFIG. 1B) may be adjusted to regulate an amount of heating/charging ofthe battery. Too increase an amount of heating of the battery, the valvemay be adjusted to a more open position and/or a speed of the pump maybe increased.

Coolant flow through the battery may be regulated by adjusting one ormore valves. Specifically, a first coolant valve positioned near aninlet of the coolant flow into the battery (e.g., valve 117 shown inFIG. 1B) may be adjusted to a second position to direct coolant from acoolant system (e.g., coolant circuit 102 shown in FIG. 1B) into thebattery. As the first coolant valve is adjusted towards an open secondposition away from a closed first position an amount of coolant directedthrough the battery may increase. Additionally, in some examples, asecond coolant valve may be included near an outlet of the coolant flowout of the battery, and may therefore be adjusted to regulate the amountof coolant flowing out of the battery. Specifically, the second coolantvalve may be adjusted between a closed first position, wheresubstantially zero coolant may flow out of the battery and an opensecond position where coolant flows out of the battery. Thus, in thedescription of FIGS. 3-6 herein, decreasing coolant flow may be achievedby one or more of adjusting the first coolant valve and/or secondcoolant valve towards their respective first closed positions.Conversely, increasing coolant flow through the battery may be achievedby one or more of adjusting one or more of the first and second coolantvalves towards their respective second open positions. Flowing coolantthrough the battery may discharge/cool the battery, as the coolant maybe at a lower temperature than the battery.

Instructions for executing method 300 and all other methods describedherein with reference to FIGS. 4-6 may be stored in the memory of acontroller (e.g., controller 12 shown in FIGS. 1A and 1B). Therefore,method 300 and all other methods described herein may be executed by thecontroller based on the instructions stored in the memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIGS. 1A and 1B. The controller may send signals to one or more of theheat source pump, heat source valve, first coolant valve, and secondcoolant valve to adjust an amount of heating and/or cooling of thebattery and coolant.

Method 300 begins at 302 which comprises estimating and/or measuringengine operating conditions. Engine operating conditions may include acoolant temperature, a coolant mass flow, a state of charge of thethermal battery, exhaust gas temperature, a speed of the heat sourcepump, positions of the one or more valves, etc.

After estimating and/or measuring engine operating conditions at 302,method 300 may proceed to 304 which comprises estimating a state ofcharge of the battery. Methods for estimating the state of charge of thebattery are described below with reference to FIGS. 4-6. In someexamples, estimating and/or measuring the state of charge of the batterymay comprise stopping coolant flow through the battery and waiting aduration for thermal equilibrium in the battery to be reached betweenthe coolant and the components of the battery as described below withreference to FIG. 5. Then, coolant flow may resume, and a temperature ofthe stagnant coolant may be measured as it exits the battery. Based onthe coolant temperature, a state of charge of the battery may beestimated. However, in other examples, as described below with referenceto FIG. 4, the state of charge of the battery may be estimatedopportunistically whenever the components of the battery and the coolanthave reached thermal equilibrium with one another.

Method 300 may then continue from 304 after estimating the state ofcharge of the battery to 306, where the method 300 may comprisedetermining if battery charging is desired. For example, the method 300at 306 may comprise determining if the state of charge of the battery isbelow a threshold. The threshold may represent a state of charge of thebattery corresponding to a temperature of the battery that is below thephase change temperatures of one or more PCMs included in the battery.Thus, if the state of charge of the battery is less than the threshold,then battery charging may be desired at 306. However, in other examples,determining if battery charging is desired at 306 may be based on one ormore of a temperature of exhaust gasses, temperature of coolant, enginecold start conditions, and/or a rate of charging or discharging of thebattery. For example, if cabin warming is predicted, and an increase incoolant temperature is therefore expected, the battery may preemptivelybe charged in anticipation of the cabin warming procedure. In otherexamples, if exhaust gas temperature is expected to decrease in futuredriving conditions, the battery may opportunistically be charged whilethe exhaust gasses are hotter.

If it is determined that battery charging is desired, then method 300may proceed from 306 to 308, which may comprise increasing heat transferto the battery. Specifically, the method 300 at 308 may compriseincreasing power supplied to the heat source pump, to increase the pumpspeed, and therefore increase fluid flow and therefore heat transfer,between the exhaust and the battery. Additionally or alternatively, themethod 300 at 308 may comprise increasing an opening formed by the heatsource valve to increase fluid flow between the exhaust and battery. Inthis way, an amount of thermal energy transferred from the exhaust tothe thermal battery may be increased.

Method 300 may then continue from either 308 or from 306 if it isdetermined at 306 that battery charging is not desired, to 310, whichcomprises estimating a temperature of coolant exiting the battery. Thetemperature of the coolant may be estimated based on outputs from atemperature sensor (e.g., temperature sensor 112 shown in FIGS. 1B-2E)positioned near a coolant outlet of the battery.

After estimating the coolant temperature, the method 300 may thencontinue from 310 to 312 which may comprise determining if coolantwarming is desired. Coolant warming may be desired when the estimatedcoolant temperature is less than a desired coolant temperature. Adesired coolant temperature may be determined based on engine operatingconditions, such as engine temperature, cabin temperature, etc. Forexample, in response to an increase in desired cabin temperature, thedesired coolant temperature may increase.

If the coolant temperature is less than desired and coolant warming isdesired, method 300 may proceed from 312 to 314 which comprisesincreasing coolant flow through the battery. As described above, one ormore of the first coolant valve and/or second coolant valve may beopened to increase coolant flow through the battery. Due to theincreased coolant flow through the battery, the temperature of thecoolant may be increased. Further, the rate of warming of the coolantmay increase.

However, if at 312 it is determined that coolant warming is not desired,then method 300 may proceed from 312 to 316 which comprises decreasingcoolant flow through the battery. As described above, one or more of thefirst coolant valve and/or second coolant valve may be closed todecrease coolant flow through the battery. Due to the decreased coolantflow through the battery, the temperature of the coolant may bemaintained and/or decreased. In some examples, the rate of warming ofthe coolant may be reduced. In yet further examples, the method 300 at316 may comprise stopping coolant flow through the battery. In otherexamples, the method 300 at 316 may comprise maintaining coolant flow atits current flow rate. After executing either 314 or 316, method 300 maythen return.

Turning now to the methods shown in FIGS. 4-6, they describe exampleroutines for estimating a state of charge of the battery described abovewith reference to FIG. 3. Thus, any one or more of the methods describedin FIGS. 4-6 may be incorporated and/or executed at 302 of method 300shown in FIG. 3. FIG. 4 describes an example approach where the state ofcharge of the battery may opportunistically be estimated whenevercoolant flow through the battery has stagnated. Specifically, the stateof charge of the battery may be estimated based on a temperature ofcoolant exiting the battery when coolant flow through the batteryresumes. The method described in FIG. 5 provides for an active state ofcharge estimate, where coolant flow through the battery is temporarilyhalted, and then allowed to resume. Similar to the method described inFIG. 4, the coolant temperature may be measured as the coolant exits thebattery, and a state of charge estimate may be determined based on thecoolant temperature. Finally, FIG. 6 describes an approach wheretemperatures of different PCMs (e.g., PCMs 220 and 224 shown in FIGS. 2Band 2C) in the battery are monitored, and based on changes in thetemperature of the PCMs, a state of charge estimate is made.

Focusing now of FIG. 4, the method 400 begins at 402 by determining ifthe coolant flow rate through the battery is less than a threshold. Insome examples, the threshold may be approximately zero. Thus, in someexamples, the method 400 at 402 may comprise determining if coolant isnot flowing through the battery. However, in other examples, thethreshold may be greater than zero. It is important to note that avolume/mass of coolant may be held inside the battery, even whilecoolant flow through the battery is zero. Thus, when coolant flowthrough the battery stops, the coolant in the battery may remain in thebattery, until coolant flow resumes, and the stagnant coolant exits thebattery. Coolant flow rate through the battery may be estimated based onone or more of a position of the first coolant valve, a position of thesecond coolant valve, and/or a speed of a coolant pump (e.g., pump 133shown in FIG. 1B).

If the coolant flow rate is not less than the threshold at 402, such asduring conditions where coolant warming is desired, method 400 may thenreturn, and an estimate of the state of charge of the battery may not bemade. Thus, in some examples, the state of charge of the battery may notbe estimated when coolant flow through the battery is greater than thethreshold. Said another way, the state of charge of the battery may notbe estimated when the coolant and battery have not reached thermalequilibrium and/or components of the battery have not reached thermalequilibrium.

However, in other examples, the method 402 may continue from 402 tooptional step 404 which comprises measuring the coolant temperature,even when coolant flow through the battery is greater than thethreshold. The coolant temperature may be measured based on outputs fromthe temperature sensor as described above with reference to 310 of FIG.3. After estimating the coolant temperature at 404, method 400 mayproceed to optional step 406 which comprises estimating the state ofcharge of the thermal battery based on one or more of the coolanttemperature, internal heat transfer within the battery, thermalcapacitance of one or more components of the battery and coolant, phasechange temperatures of the PCMs, latent heat capacities of the PCMs, andmasses of the PCMs. Method 400 then returns.

Returning to 402 if it is determined that the coolant flow rate throughthe battery is less than the threshold, method 400 may proceed from 402to 408, which comprises determining a duration to thermal equilibrium ofthe battery and coolant based on a most recent coolant temperaturemeasurement and a most recent state of charge estimate of the battery.Thus, the method 400 at 408 may comprise determining an amount of timeuntil the battery components and/or coolant in the battery will reachthermal equilibrium, where the temperature of the components of thebattery and/or coolant are approximately the same temperature. The timeto thermal equilibrium may increase for greater differences in thecoolant temperature and the temperature of the battery, greater rates ofchange in the temperature of the battery, greater differences intemperatures of internal components of the battery, etc. Further, whenPCMs included in the battery are above, or below their phase changetemperatures, the time to thermal equilibrium may be less than when thePCMs are undergoing a phase change.

After determining the time to thermal equilibrium of the battery and thecoolant, method 400 may continue from 408 to 410, which comprisesdetermining if the coolant flow rate has remained below the thresholdfor the duration of the time to thermal equilibrium. More simply, themethod at 410 comprises determining if coolant flow through the batteryhas stopped for a sufficient amount of time to allow for the coolant andbattery components to achieve thermal equilibrium. If the time tothermal equilibrium has not been reached, and therefore the batterycomponents and coolant in the battery are not in thermal equilibrium,then method 400 may continue from 410 to 412 which comprises waiting theduration until thermal equilibrium is reached.

After waiting for the duration to thermal equilibrium, method 400 maythen continue from 412 to 414 which comprises determining if the coolantflow rate is less than the threshold in the same or similar mannerdescribed above with reference to 402. If the coolant flow rate hasincreased above the threshold while waiting for thermal equilibrium inthe battery to be reached, then method 400 may return from 414, and anestimate of the state of charge of the battery may not be obtained.However, in other examples, method 400 may proceed from 414 to 404 and406 in the manner described above, if the coolant flow is greater thanthe threshold after waiting for thermal equilibrium to be reached.

However, if it is determined at 414 that coolant flow remains below thethreshold after waiting for thermal equilibrium in the battery to bereached, method 400 may then proceed from 414 to 416 which comprisesincreasing coolant flow through the battery and measuring thetemperature of the coolant in the same or similar manner to thatdescribed above with reference to 310 of FIG. 3. Alternatively, if at410, the time to thermal equilibrium has already expired and the coolantflow is less than the threshold, then method 400 may proceed directly to416 from 410. Thus, the temperature of the coolant may be taken once thecoolant in the battery, and internal components of the battery havereached thermal equilibrium. As described above, in some examplescoolant flow may be completely stopped prior to execution of 416. Thus,increasing coolant flow through the battery at 416 may compriseinitiating coolant flow through the battery, for example by adjustingone or more of the first and second coolant valves away from closedpositions.

After increasing coolant flow through the battery at 416, method 400 maycontinue to 418 which comprises determining if the battery is charging.Said another way, the method 400 at 418 may comprise determining if theenthalpy of the battery is increasing and/or the temperature of thebattery is increasing. Determining whether the battery is charging maybe based on a most recent of most recent set of temperatures and/orstate of charge estimates for the battery. Based on the trend intemperatures and/or state of charge of the battery, it may be determinedif the battery is charging or discharging. However, in other examples,determining if the battery is charging or discharging may be based on bebased on one or more of a position of the heat source valve, a speed ofthe heat source pump, and positions of one or more of the first coolantvalve and second coolant valve. For example, if one or more of the firstcoolant valve and second coolant valve are closed, and coolant is notcirculating through the battery, and the heat source pump is on and theheat source valve is open, then the enthalpy of the battery may beincreasing due to the thermal energy being absorbed from exhaust gassesby internal components of the battery, and as such it may be determinedthat the battery is charging. Conversely, if the heat source pump isoff, and/or the heat source valve is closed, and coolant is circulatingthrough the battery, it may be determined that the battery isdischarging.

If it is determined at 418 that the battery is not charging (e.g.,discharging), then method 400 may continue from 418 to 420 whichcomprises determining the state of charge of the thermal battery basedon the coolant temperature and one or more chemical properties of thetwo PCMs. The chemical properties may include one or more of internalheat transfer rates, diffusion rates, time to molecular alignment,specific heat, phase change temperatures of the PCMs, latent heatcapacities of the PCMs, masses of the PCMs, ambient pressure, altitude,and coolant system pressure. Additionally, a first transfer function maybe applied to the input received from the temperature sensor, and mayconvert the coolant temperature estimate received from the sensor to anestimate of the state of charge of the battery. The first transferfunction may be a non-linear transfer function that relates thetemperature of the coolant to a state of charge of the battery. Thus,the controller may use a look-up table to convert the coolanttemperature reading (e.g., inputs received from the temperature sensor)to a state of charge estimate based on the first transfer function.However, in other examples, the first transfer function may be a lineartransfer function. The first transfer function may correspond to a knownrelationship between coolant temperatures and states of charge of thebattery while the battery is discharging.

However, if it is determined at 418 that the battery is charging, thenmethod 400 may continue from 418 to 422 which comprises determining thestate of charge of the battery based on the measured coolant temperatureand one or more chemical properties of the two PCMs. The chemicalproperties may include one or more of internal heat transfer rates,diffusion rates, time to molecular alignment, specific heat, phasechange temperatures of the PCMs, latent heat capacities of the PCMs, andmasses of the PCMs, ambient pressure, altitude, and coolant systempressure. Additionally, a second transfer function may be applied to theinput received from the temperature sensor, and may convert the coolanttemperature estimate to an estimate of the state of charge. The secondtransfer function may be a non-linear transfer function. However, inother examples the second transfer function may be a linear transferfunction. The second transfer function may be different than the firsttransfer function. Specifically, the second transfer function mayconvert coolant temperatures (e.g., inputs received from the temperaturesensor) to a state of charge for the battery along a known chargingcurve. That is, the state of charge of the battery for a given coolanttemperature may be different depending on whether the battery ischarging or discharging. Thus, a different transfer function may be usedto determine the state of charge of the battery when the battery ischarging than when the battery is discharging. Method 400 may thenreturn from either 420 or 422.

Turning now to FIG. 5, it shows a second example method 500 fordetermining the state of charge of the battery described above withreference to FIG. 3. However, in the method 500, coolant flow may beactively stopped for a duration until the battery and coolant reachthermal equilibrium, and then coolant flow through the battery mayresume, and a temperature measurement of the coolant may be taken andused to infer a state of charge of the battery.

Method 500 begins at 502 which comprises determining if it is desired toestimate the state of charge of the thermal battery. For example, it maybe desired to determine the state of charge of the battery when morethan a threshold duration has passed since the most recent state ofcharge estimate. Thus, estimates of the state of charge of the batterymay be performed at regular intervals. However, in further examples therate at which the state of charge of the battery is estimated may bebased on one or more of the state of charge of the battery, thetemperature of the coolant, the rate of charging and/or discharging ofthe battery, exhaust gas temperature, changes in desired coolanttemperature, etc. In other examples, it may be desired to estimate thestate of charge of the battery when the desired coolant temperaturechanges, and/or when exhaust gas temperatures change by more than athreshold, etc.

If it is determined at 502 that a state of charge estimate of thebattery is not desired, then method 500 may continue from 502 to 504which comprises continuing to flow coolant through the thermal batteryas desired to achieve the desired coolant temperature. Method 500 maythen return.

However, if it is determined at 502 that a state of charge estimate isdesired for the battery, then method 500 may proceed from 502 to 506which comprises reducing coolant flow through the battery to a thresholdflow rate. In some examples, the threshold flow rate may beapproximately zero. Thus, the method 500 at 506 may comprise stoppingcoolant flow through the battery. However, in other examples, thethreshold flow rate at 506 may be greater than zero.

After reducing coolant flow through the battery to the threshold flowrate at 506, method 500 may continue from 506 to 508 which comprisesdetermining the duration to thermal equilibrium of the battery andcoolant in the battery based on a most recent coolant temperaturemeasurement and/or a state of charge estimate of the battery, in thesame or similar manner described above with reference to 408 in FIG. 4.Thus, the method at 506 may comprise determining an amount of time tocontinue to halt coolant flow through the battery.

Method 500 may then continue to 510 from 508, where the method at 510may comprise waiting the duration. Thus, the method at 500 may comprisecontinuing to prevent coolant flow through the battery for the duration.More simply the method 500 at 510 may comprise stagnating coolant in thethermal battery until the coolant and components of the thermal batteryreach thermal equilibrium. Specifically, the method 500 at 510 maycomprise adjusting one or more of the first coolant valve and/or secondcoolant valve to their respective closed first positions. In this way,the method 500 at 510 may comprise stopping coolant flow through thebattery for the duration.

After waiting the duration at 510, method 500 may then continue to 512which comprises increasing coolant flow through the battery andmeasuring a temperature of the coolant as it exits the battery in thesame or similar manner to that described above with reference to 416 inFIG. 4.

Method 500 may then continue from 512 to 514 after measuring coolanttemperature as it exits the thermal battery, where the method 500 at 514comprises determining if the battery is charging in the same or similarmanner to that previously described above with reference to 418 in FIG.4. If the battery is not charging, then method 500 may continue from 514to 516 which comprises determining the state of charge of the batterybased on the measured coolant temperature and one or more chemicalproperties of the PCMs, in the same or similar manner to that describedabove with reference to 420 in FIG. 4. However, if the battery ischarging, then method 500 may continue from 514 to 518 which comprisesdetermining the state of charge of the battery based on the measuredcoolant temperature and one or more chemical properties of the PCMs inthe same or similar manner to that described above with reference to 422in FIG. 4. Method 500 may then return from either 516 or 518.

Turning now to FIG. 6, it shows a third example method 600 fordetermining the state of charge of the battery described above withreference to FIG. 3 when a first PCM (e.g., PCM 220 shown in FIGS. 2Band 2C) and second PCM (PCM 224 shown in FIGS. 2B and 2C) with differentphase change temperatures are separated from one another in distinctbattery cells (e.g., cells 218 and 222 shown in FIGS. 2B and 2C) in thebattery. In the method 600, a state of charge of the battery may beestimated based on changes in the temperature of one or more PCMs.Specifically, when one of either the first PCM or the second PCM isundergoing a phase change, the temperature of the PCM not undergoing thephase change may be used to estimate a state of charge of the battery.Since the PCMs may be separated from one another into distinct cells,heat transfer between the PCMs may not be instantaneous. As such, whenone of the PCMs is undergoing a phase change at an approximatelyconstant temperature, the other PCM may continue to change temperature.Based on the temperature of the PCM not undergoing the phase, anestimate of the enthalpy level of the PCM undergoing the phase changemay be obtained, and therefore a more accurate measurement of the stateof charge of the battery may be made.

Method 600 may begin at 602 which comprises monitoring the temperaturesof the first and second PCMs. In some examples, the temperatures of thefirst and second PCMs may be monitored via outputs from PCM temperaturesensors (e.g., temperature sensors 230 and 232 shown in FIGS. 2B and 2C)positioned in the battery cells containing the PCMs. In such examples,it is important to note that the temperatures of the PCMs maycontinuously be monitored, and as such, the controller may execute 602while executing the rest of method 600. In other examples, thetemperatures of the first and second PCMs may be estimates based onoutputs from a coolant outlet temperature sensor (e.g., temperaturessensor 112 shown in FIGS. 2A-2E) positioned in a coolant outlet.

From 602, method 600 may proceed to 604 which comprises determining ifthe battery is charging in the same or similar manner to that describedabove with reference to 418 shown in FIG. 4. However, in other examples,the method 600 at 604 may comprise determining if the battery ischarging based on temperature changes in one or more of the PCMs. Thus,if the temperatures of one or more of the PCMs are decreasing, then itmay be determined that the battery is discharging. However, if thetemperatures of one or more of the PCMs are increasing then it may bedetermined at 604 that the battery is charging.

If the battery is charging at 604, method 600 may continue from 604 to606 which comprises determining if the first PCM is at its phase changetemperature. Thus, the method 600 at 606 may comprise determining if thefirst PCM is undergoing a phase change based on the temperature of thefirst PCM and a known phase change temperature of the first PCM. If thetemperature of the first PCM is approximately the same as its phasechange temperature, then it may be determined at 606 that the PCM isundergoing a phase change.

If it is determined that the first PCM is at its phase changetemperature at 606, then method 600 may continue from 606 to 608 whichcomprises estimating a state of charge of the battery based on thetemperature of the second PCM, one or more chemical properties of thePCMs, heat transfer within the battery including conduction and/orconvention rates, and a first transfer function. The first transferfunction may in some examples be a non-linear transfer function.However, in other examples, the first transfer function may be a lineartransfer function. The first transfer function may convert the input ofthe second PCM temperature measurement to an output corresponding to anestimate of the state of charge of the battery. Method 600 then returns.

However, if it is determined at 606 that the first PCM is not at itsphase change temperature, then method 600 may proceed from 606 to 610which comprises determining if the second PCM is at its phase changetemperature. Thus, the method 600 at 610 may comprise determining if thesecond PCM is undergoing a phase change based on the temperature of thesecond PCM and a known phase change temperature of the second PCM. Ifthe temperature of the second PCM is approximately the same as its phasechange temperature, then it may be determined at 610 that the second PCMis undergoing a phase change.

If it is determined that the second PCM is at its phase changetemperature at 610, then method 600 may continue from 610 to 612 whichcomprises estimating a state of charge of the battery based on thetemperature of the first PCM, one or more chemical properties of thePCMs, heat transfer within the battery including conduction and/orconvention rates, and a second transfer function. The second transferfunction may in some examples be a non-linear transfer function.However, in other examples, the second transfer function may be a lineartransfer function. The second transfer function may convert the input ofthe first PCM temperature measurement to an output corresponding to anestimate of the state of charge of the battery. Method 600 then returns.

However, if it is determined at 610 that the temperature of the secondPCM is not at its phase change temperature, then method 600 may continueto 614 which comprises determining a state of charge of the batterybased on the temperatures of the first PCM and second PCM, one or morechemical properties of the PCMs, heat transfer within the batteryincluding conduction and/or convention rates, and a third transferfunction. Said another way, based on the temperatures of the first andsecond PCMs, the controller may determine the state of charge of thebattery based on a look-up table relating states of charge of thebattery to PCM temperatures when the battery is charging. Method 600 maythen return.

Returning to 604, if it is determined that the battery is discharging,method 600 may continue from 604 to 616 which comprises determining ifthe first PCM is at its phase change temperature in the same or similarmanner to that described above at 606.

If it is determined at 616 that the first PCM is at its phase changetemperature, then method 600 may continue from 616 to 618 whichcomprises estimating a state of charge of the battery based on thetemperature of the second PCM, one or more chemical properties of thePCMs, heat transfer within the battery including conduction and/orconvention rates, and a fourth transfer function. Method 600 thenreturns.

However, if it is determined at 616 that the first PCM is not at itsphase change temperature, then method 600 may proceed from 616 to 620which comprises determining if the second PCM is at its phase changetemperature in the same or similar manner to that described above at610.

If it is determined that the second PCM is at its phase changetemperature at 620, then method 600 may continue from 620 to 622 whichcomprises estimating a state of charge of the battery based on thetemperature of the first PCM, one or more chemical properties of thePCMs, heat transfer within the battery including conduction and/orconvention rates, and a fifth transfer function. Method 600 thenreturns.

However, if it is determined at 620 that the temperature of the secondPCM is not at its phase change temperature, then method 600 may continueto 624 which comprises determining a state of charge of the batterybased on the temperatures of the first PCM and second PCM, one or morechemical properties of the PCMs, heat transfer within the batteryincluding conduction and/or convention rates and a sixth transferfunction. Said another way, based on the temperatures of the first andsecond PCMs, the controller may determine the state of charge of thebattery based on a look-up table relating states of charge of thebattery to PCM temperatures when the battery is discharging. Method 600may then return.

Turning now to FIG. 7, it shows a graph 700 depicting changes in coolantflow through a thermal battery (e.g., battery 202 shown in FIGS. 2A-2E)during varying engine operating conditions. Specifically, changes incoolant flow through the battery are shown at plot 702. As describedabove with reference to FIGS. 1B and 3-6, coolant flow through thebattery may be adjusted by adjusting the position of one or more valvepositioned near a coolant inlet and/or coolant outlet of the battery.Further, the coolant flow rate through the battery may be estimatedbased on the positions of one or both of the coolant valves. The stateof charge of the battery is shown at plot 504. Estimates of the state ofcharge of the battery may be obtained based on a temperature of thecoolant taken proximate a coolant outlet of the battery as the coolantexits the battery. A position of a heat source valve (e.g., valve 120shown in FIG. 1B) is shown at plot 506. The heat source valve may beopened to circulate a fluid between an exhaust passage (e.g., exhaustpassage 48 shown in FIGS. 1A and 1B) and the thermal battery fortransferring thermal energy from the warmer exhaust gasses to the coolerthermal battery. Specifically, the heat source valve may be adjustedbetween a closed first position, where approximately no fluid flowsthere-through and thus, substantially no heat is transferred to thethermal battery, and an open second position where fluid flows throughthe valve and thus, heat is added to the thermal battery. Plot 508depicts a difference in temperature between the coolant in the battery,and a temperature of one or more PCMs (e.g., PCMs 220 and 224 shown inFIGS. 2B and 2C) included in the battery.

Beginning before t₁, coolant may be flowing through the battery, and theheat source valve may be closed. As such, the state of charge of thebattery may be decreasing, as the coolant may draw thermal energy fromthe battery as the coolant flows through the battery. Further, thecoolant may be at a substantially different temperature than the PCM ofthe battery.

At t₁, a state of charge estimate of the battery may be desired, and assuch, coolant flow through the battery may be stopped. Thus, coolantflow at t₁, may be reduced to approximately zero. As such, the state ofcharge of the battery may begin to level off and/or stop discharging.The heat source valve may remain closed, and the difference intemperature of the coolant and PCM may continue to decrease.

Between t₁ and t₂, coolant flow through the battery may remain stagnant,and the state of charge of the battery may remain approximately thesame. Further, the heat source valve may remain closed, and thedifference in temperature between the coolant and PCM may continue todecrease. At t₂, the difference in temperature between the coolant andPCM may reach a threshold 709. The threshold 709 may in some examples beapproximately zero, and thus may represent conditions where the coolanttemperature of coolant in the thermal battery, and the temperature ofthe PCM of the battery are approximately the same. Thus, the threshold709 may represent thermal equilibrium of internal battery components andthe coolant in the battery. However, in other examples, the threshold709 may be greater than zero.

Thus, at t₂ when thermal equilibrium has been reached within thebattery, coolant flow through the battery may be turned back on byopening one or more of the coolant valves. As the coolant that hasreached thermal equilibrium with the internal battery components leavesthe battery at t₂, a temperature of the coolant may be measured via atemperature sensor (e.g., temperature sensor 112 shown in FIGS. 1B-2E),and a state of charge of the battery may be estimated based on thecoolant temperature as it exits the battery. The heat source valve mayremain closed at t₂.

Between t₂ and t₃, coolant may continue to flow through the battery, andthus the state of charge of the battery may decrease. The heat sourcevalve may remain closed, and the temperature difference between thecoolant and the PCM may initially increase, as coolant flow through thebattery resumes, and may begin to decrease, as coolant warms to thetemperature of the battery. At t₃, the coolant temperature may reach adesired coolant temperature, and therefore coolant flow through thebattery may no longer be desired.

Thus, coolant flow may be turned off at t₃, and as such, the battery maystop discharging at t₃. The heat source valve may remain closed at t₃,and the coolant in the battery may continue to warm to the temperatureof the PCM in the battery. Between, t₃ and t₄, coolant warming by thethermal battery may continue to not be desired. The difference intemperature between the coolant and the battery may continue todecrease, as the stagnant coolant in the battery may reach thermalequilibrium with the battery. Thus, the temperature of the coolant mayreach approximately the same temperature as the PCM in the batterybetween t₃ and t₄. The heat source valve may remain closed, and thus thestate of charge of the battery may remain relatively constant.

At t₄, warming of the coolant by the thermal battery may be desired, andas such coolant flow through the battery may resume. Since the coolantin the battery reaches thermal equilibrium with the battery between t₃and t₄, an estimate of the state of charge of the battery may be made att₄ based on the coolant temperature as it exits the battery, in responseto coolant flow through the battery resuming. The heat source valve mayremain closed at t₄.

Between t₄ and t₅, coolant may continue to flow through the battery, andthus the state of charge of the battery may decrease. The heat sourcevalve may remain closed, and the temperature difference between thecoolant and the PCM may initially increase, as coolant flow through thebattery resumes, and may begin to decrease, as coolant warms to thetemperature of the battery. At t₅, an estimate of the state of charge ofthe battery may be desired, and as such, coolant flow through thebattery may be stopped at t₅. The heat source valve may remain closed att₅, and the difference in temperature between the coolant and thebattery may decrease, as the coolant in the battery may be warmed by thebattery.

Between, t₅ and t₆, coolant flow through the battery may remain off. Thedifference in temperature between the coolant and the battery maycontinue to decrease, as the stagnant coolant in the battery may reachthermal equilibrium with the battery. Thus, the temperature of thecoolant may reach approximately the same temperature as the PCM in thebattery between t₅ and t₆. The heat source valve may remain closed, andthus the state of charge of the battery may remain relatively constant.

At t₆, coolant flow may through the battery may resume in response tothe coolant in the battery reaching thermal equilibrium with thebattery. As the coolant flows out of the battery, a temperature of thecoolant may be measured, and an estimate of the state of charge of thebattery may be determined. The state of charge of the battery maydecrease below a threshold state of charge 705. In response to theestimated state of charge decreasing below the threshold 705 at t₆, theheat source valve may be opened at t₆, to transfer heat from the exhaustgasses to the battery, and therefore charge the battery. Thus, batterycharging may be initiated at t₆.

Between t₆ and t₇, coolant warming by the thermal battery may bedesired, and as such coolant flow through the battery may continue. Thetemperature difference between the coolant and the PCM may initiallyincrease, as coolant flow through the battery resumes, and may thendecrease, as coolant warms to the temperature of the battery. The heatsource valve may remain open between t₆ and t₇, and the state of chargeof the battery may therefore increase. However, since coolant is stillflowing through the battery between t₆ and t₇, the battery may charge ata lower first rate between t₆ and t₇.

At t₇, coolant warming by the thermal battery may no longer be desired,and as such, coolant flow through the battery may stop. The heat sourcevalve may remain open, and due to the cessation of coolant flow throughthe battery at t₇, the battery may begin to charge at a higher secondrate. The temperature difference between the coolant and the battery maycontinue to decrease, as the stagnant coolant in the battery is warmedby the battery. Warming of the coolant may be enhanced due to thecharging of the battery.

Between t₇ and t₈, the state of charge of the battery may continue toincrease at the higher second rate. The heat source valve thereforeremains open, and the temperature difference between the coolant and thePCM may continue to decrease. Coolant flow remains off between t₇ andt₈.

At t₈, the battery may reach a fully charged state of charge, and inresponse to the battery reaching a fully charged state, the heat sourcevalve may be closed. Thus, charging of the battery may be stopped at t₈.Further, in response to increased desired coolant temperature at t₈,coolant flow through the battery may resume. The temperature differencebetween the coolant and the PCM may initially increase, as coolant flowthrough the battery resumes, and may then decrease, as coolant warms tothe temperature of the battery.

After t₈, coolant may continue to flow through the battery, the heatsource valve may remain closed, and thus, the state of charge of thebattery may decrease from the fully charged state. As the coolant iswarmed, the difference in temperature between the coolant and PCM maydecrease.

Thus, a thermal battery may comprise two phase change materials withdifferent phase change temperatures. When coolant included in thethermal battery and the PCMs reach thermal equilibrium, a temperature ofcoolant exiting the battery may be measured, and a state of charge ofthe battery may be estimated based on the measured coolant temperature.Specifically, coolant flow through the battery may be temporarilystopped until coolant in the battery stagnates, and both internalcomponents of the battery and the coolant within the battery reachthermal equilibrium. Then, coolant flow may resume, and a temperature ofthe stagnated coolant may be measured as it exits the battery. Based onthe coolant temperature an estimate of the state of charge of thebattery may be obtained.

In this way, a technical effect of increasing the accuracy of estimatesof the state of charge of a thermal battery may be achieved, by stoppingcoolant flow through the battery, until thermal equilibrium within thebattery is reached, and then resuming coolant flow and measuring atemperature of the coolant as it exits the battery. In this way, thetemperature of the coolant exiting the battery may more closely matchthe actual temperature of the battery. Thus, differences between thecoolant temperature and the battery may be reduced. As such, theaccuracy of estimates of the state of charge of the battery that arebased on the temperature of coolant exiting the battery, may beincreased. By increasing the accuracy of estimates of the state ofcharge of the battery, heating efficiency, and therefore fuel economymay be increased.

In one example, a method may comprise estimating a temperature of athermal battery after the battery and coolant included therein havereached thermal equilibrium, and determining a state of charge of thebattery based on the estimated temperature and one of a first and secondtransfer functions. Additionally or alternatively, the temperature ofthe thermal battery may be estimated based on outputs from a temperaturesensor coupled to a coolant outlet of the battery, where the sensor maybe configured to measure a temperature of coolant exiting the battery.In any of the above methods or combination of methods, determining thestate of charge of the battery may be based on the estimated temperatureand the first transfer function when the battery is charging. In any ofthe above methods, the determining the state of charge of the batterymay be based on the estimated temperature and the second transferfunction when the battery is discharging. Any of the above methods orcombination of methods may further comprise, stopping coolant flowthrough the thermal battery until the thermal battery and coolantincluded therein have reached thermal equilibrium, prior to estimatingthe temperature of the thermal battery. In any of the above methods orcombination of methods, the stopping the coolant flow through thethermal battery may comprise adjusting a coolant valve to a firstposition to bypass coolant around the thermal battery. Any of the abovemethods or combination of methods may further comprise, resuming coolantflow through the thermal battery after the thermal battery and coolantincluded therein have reached thermal equilibrium. Further, the resumingcoolant flow through the thermal battery comprising adjusting a coolantvalve away from a first position to circulate coolant through thethermal battery.

In another representation, a thermal battery system may comprise athermal storage device including a first phase change material having afirst phase change temperature and a second phase change material havinga second, different phase change temperature, a coolant valve adjustablebetween a first position and a second position to selectively couple thethermal storage device to an engine coolant circuit and regulate anamount of coolant circulating through the thermal storage device, atemperature sensor for estimating a temperature of the device, and acontroller with non-transitory computer readable instructions for:estimating a temperature of the device when coolant within the devicehas stopped for more than a threshold duration, and determining a stateof charge of the battery system based on the estimated temperature andone of a first and second transfer functions. In some examples, thefirst and second phase change materials may be combined together in amixture. Additionally or alternatively, the mixture may comprise more ofone of the phase change materials than the other. However, in otherexamples, the first and second phase change materials may be separatedfrom one another into distinct battery cells. Any of the above systemsor combination of system may further comprise a heat exchange loop, theheat exchange loop disposed at least partially within an exhaust passageof an engine system and at least partially within the thermal storagedevice, the heat exchange loop comprising coolant, circulatingthere-through, for transferring thermal energy from the exhaust passageto the thermal storage device. In any of the above systems orcombination of systems, the controller may further be configured withinstructions stored in memory for: in response to a request for anestimate of the state of charge of the device, stopping coolant flowthrough the device for a duration, resuming coolant flow after waitingthe duration, and estimating a state of charge of the battery based on atemperature of the coolant as it exits the device via output from atemperature sensor positioned near a coolant outlet of the device. Inany of the above systems or combination of systems, the duration may bean amount of time for coolant included within the device, and internalcomponents of the device including the phase change materials, to reachthermal equilibrium, and where the duration may be calculated based on amost recent coolant temperature measurement and a most recent state ofcharge estimate of the battery.

In yet another representation, a method for an engine cooling system maycomprise stopping coolant flow through a thermal storage devicecomprising two phase change materials with different melting points fora duration, resuming coolant flow through the thermal storage deviceafter the duration and estimating a temperature of coolant exiting thethermal storage device based on outputs from a temperature sensorpositioned proximate a coolant outlet of the device, and calculating astate of charge of the device based on the estimated coolant temperatureand one of a first and second transfer functions. Additionally, theduration may comprise an amount of time for coolant included within thedevice and internal components of the device including the phase changematerials, to reach thermal equilibrium, and where the duration may becalculated based on a most recent coolant temperature measurement and amost recent state of charge estimate of the battery. In any of the abovemethods or combination of methods, the calculating the state of chargeof the device may be based on the estimated coolant temperature and thefirst transfer function when the device is charging. In any of the abovemethods or combination of methods, the calculating the state of chargeof the device may be based on the estimated coolant temperature and thesecond transfer function when the device is discharging. Any of theabove methods or combination of methods may further comprise estimatinga state of charge of the device when the device and/or coolant includedwithin the device are not in thermal equilibrium based on one or more ofa temperature of the coolant as it exits the device, a third transferfunction, internal heat transfer within the device, phase changetemperatures of the phase change materials, latent heat capacities ofthe phase change materials, masses of the phase change materials,ambient pressure, altitude, and coolant system pressure.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for operating a thermal storagedevice of an engine cooling system, comprising: flowing each of acoolant and a second fluid through the thermal storage device viaseparate tubes, the second fluid heated from exhaust gases of an engine;stopping the coolant flow through the thermal storage device, thethermal storage device comprising two phase change materials withdifferent melting points, for a duration; resuming coolant flow throughthe thermal storage device after the duration and estimating atemperature of coolant exiting the thermal storage device based onoutputs from a temperature sensor positioned at a coolant outlet of thethermal storage device; and calculating a state of charge of the thermalstorage device based on the estimated coolant temperature and one ormore chemical properties of the phase change materials, the thermalstorage device adapted to charge via receiving thermal energy from theheated second fluid and discharge via transfer of thermal energy to thecoolant.
 2. The method of claim 1, wherein the stopping the coolant flowis responsive to a desire to estimate the state of charge of the thermalstorage device, wherein the duration comprises an amount of time forcoolant included within the thermal storage device and internalcomponents of the thermal storage device including the phase changematerials, to reach thermal equilibrium, and wherein the duration iscalculated based on a most recent coolant temperature measurement and amost recent state of charge estimate of the thermal storage device. 3.The method of claim 1, wherein the calculating the state of charge ofthe thermal storage device is based on the estimated coolant temperatureand a first transfer function when the thermal storage device ischarging, the first transfer function corresponding to a knownrelationship between coolant temperature and the state of charge of thethermal storage device while the thermal storage device is charging, andwherein the calculating the state of charge of the thermal storagedevice is executed via a controller according to computer readableinstructions stored in non-transitory memory of the controller.
 4. Themethod of claim 1, wherein the calculating the state of charge of thethermal storage device is based on the estimated coolant temperature anda second transfer function when the thermal storage device isdischarging, the second transfer function corresponding to a knownrelationship between the coolant temperature and the state of charge ofthe thermal storage device while the thermal storage device isdischarging, and further comprising, while flowing the coolant throughthe thermal storage device, adjusting the coolant flow based on adesired coolant temperature, the desired coolant temperature based onengine operating conditions of the engine.
 5. The method of claim 1,further comprising estimating the state of charge of the thermal storagedevice when the thermal storage device and/or coolant included withinthe thermal storage device are not in thermal equilibrium based on oneor more of a temperature of the coolant as it exits the thermal storagedevice, a third transfer function, internal heat transfer within thethermal storage device, phase change temperatures of the phase changematerials, latent heat capacities of the phase change materials, massesof the phase change materials, ambient pressure, altitude, and coolantsystem pressure.